Field of the Invention
This disclosure relates to systems for simulating the diagnostic features of tension pneumothorax and cardiac tamponade, and more particularly, systems for simulating the diagnostic features of tension pneumothorax and cardiac tamponade within a medical training manikin.
Description of Related Art
Manikins are often used in the medical profession as simulation aids for training nurses, doctors and medics to perform diagnostic and therapeutic procedures. Multiple different types of manikins are used in patient care training courses on topics such as Basic Life Support (BLS), Advanced Cardiac Life Support (ACLS), Advanced Trauma Life Support (ATLS), Pediatric Advanced Life Support (PALS) and Pre-hospital Trauma Life Support (PHTLS). In all of these courses involving emergency interventions for life support, an important element is training in the diagnosis and management of tension pneumothorax and cardiac tamponade (sometimes termed pericardial tamponade).
Tension pneumothorax is a major cause of death in civilian trauma victims, in combat casualties, and in critically ill, hospitalized patients such as those in intensive care units. The condition affects patients of all ages from neonates to the very elderly. It most commonly occurs when there is a leakage of air from the surface of an injured lung that cannot escape through the chest wall. A buildup of pressure outside the lung, but inside the chest cavity, causes pressure on the lung and on the large veins within the chest. The pressure on one side of the chest displaces the structures in the mediastinum which separates the two pleural cavities of the thorax. The trachea, which lies in the mediastinum is displaced away from the pressurized side causing a characteristic diagnostic finding, namely tracheal deviation. The pressure on the major veins within the mediastinum interferes with filling of the heart, causing a progressive drop in blood pressure and eventual cardiac arrest. The drop in blood pressure is associated with acceleration in the heart rate triggered by a reflex in an effort to overcome subnormal filling pressure of the heart. In other words, the heart pumps at an accelerated rate but with a subnormal volume ejected for each cardiac contraction.
Pressure on the major veins within the mediastinum also blocks the blood from the neck veins that normally flows into the large veins of the chest. This obstruction produces a characteristic diagnostic finding of distention of the veins in the neck.
The pressure-induced collapse of the lung on the pressurized side produces the third characteristic finding of tension pneumothorax, namely the absence of audible breath sounds in the affected side of the chest. These findings, in association with a fall in blood pressure and cardiac output, and an increased heart rate and weakened pulse constitute the usual diagnostic features for tension pneumothorax.
A second lethal condition that produces some physical examination signs similar to those associated with tension pneumothorax is cardiac tamponade. This condition, like tension pneumothorax, can cause severe, rapid circulatory failure and death. It commonly occurs as the result of a leakage of blood from an injury of the heart into the pericardium (a sac surrounding the heart), causing a buildup of pressure on the cardiac chambers. This pressure prevents the heart from filling and causes a backup of blood in the great veins. This is associated with distention of the neck veins. Because the heart cannot fill, it is not able to pump normally. Again, the heart rate speeds up in a compensatory effort. However, cardiac output and blood pressure fall and cardiac arrest ultimately results.
Tension pneumothorax and cardiac tamponade can both occur in similar settings and, because they require different treatments, their disambiguation is of great importance. The treatment for tension pneumothorax is to insert a large needle or tube between the ribs into the chest cavity to provide an exit for the pressurized air. This decompresses the lungs and relieves pressure on the major mediastinal veins, and restores the cardiac output.
Cardiac tamponade, on the other hand, requires the decompression of the pericardium by inserting a needle under the sternum (breastbone) and into the pericardium to draw off blood that is exerting pressure on the heart. This decompression must be performed in such a way as not to further injure the heart. If the decompressing needle actually contacts the surface of the heart, the electrocardiogram attached to the needle displays a so-called “injury current”. As an alternative to needle decompression, the pericardium sometimes must be surgically opened through an incision in the chest or in the upper abdomen to permit decompression of the pericardium through the diaphragm.
Diagnosis of both tension pneumothorax and cardiac tamponade is based principally on a clinical examination of the patient, and particularly examination of the patient's neck and chest by the health care practitioner using his/her eyes, ears and hands. The findings on physical examination are particularly important when the condition has occurred in a casualty outside a hospital setting. Within the hospital setting, electronic monitors, displaying the patient's heart rate, blood pressure, central venous pressure, cardiac output, airway pressure, blood oxygen saturation and similar physiologic parameters are employed to monitor the clinical course of severely ill patients. Deterioration in the cardiovascular or respiratory status of the patient may be reflected by such monitoring. Since the deterioration may be caused by tension pneumothorax or cardiac tamponade, or by something else, a physical examination of the patient, occasionally combined with ultrasound studies, is carried out to secure a correct diagnosis. Treatment must urgently follow diagnosis. Recovery of the patient following correct treatment of the underlying cause of the cardiovascular/respiratory derangement is reflected not only by a reversal of the abnormal findings on physical examination of the neck and chest but also by the normalizing trend of the monitored physiologic parameters.
Suspicion of tension pneumothorax or cardiac tamponade in conscious patients is often raised by patient complaints of difficulty in breathing. The diagnosis is more difficult in unconscious patients or those who have tracheal tubes and who are receiving assisted ventilation. In these cases, a fall in blood pressure and increased heart rate trigger a focused examination of the patient to look for signs of tension pneumothorax or cardiac tamponade. The diagnosis of either of these conditions and the differentiation between the two involve the detection of distinctly abnormal findings upon physical examination of the patient's neck and chest. For example, in both conditions characteristic abnormalities include: visible distention (bulging) of the veins on both sides of the neck and rapid weak pulses palpated by the fingertips of the examiner in the patient's wrist or neck arteries. The presence of other conditions that may be associated with tension pneumothorax or cardiac tamponade, such as hemorrhagic shock, may confound the diagnostic features, for example by minimizing neck vein distention.
In the case of tension pneumothorax, in addition to the changes in the neck veins and pulses, the trachea is deviated, that is displaced, away from its normal midline position in the front of the neck. This abnormality is detectable on physical examination of the neck by palpation of the trachea in the notch at the top of the sternum (breastbone) between the heads of the clavicles (collarbones). This finding is not present in cardiac tamponade. Thus, the position of the trachea in the neck is not only an important factor in making the diagnosis of tension pneumothorax, it is also a major factor in the differential diagnosis between tension pneumothorax and cardiac tamponade.
In the case of cardiac tamponade, the presence of blood within the pericardial sac typically causes the heart sounds to be “muffled”, that is, more difficult to hear with a stethoscope.
Another physical examination finding that occurs in tension pneumothorax that is not present in tamponade, is asymmetry of the breath sounds that can be heard by an examiner listening with a stethoscope on the two sides of the chest. In tension pneumothorax, the breath sounds audible on physical examination are typically diminished or absent on the side where the abnormal pressure build-up has compressed the lung. The absence of breath sounds on one side of the chest together with the deviation of the trachea away from that side of the chest permit the accurate localization of the side of the tension pneumothorax.
Together with the findings of low blood pressure, a rapid weak pulse, bulging of the neck veins and deviation of the trachea, this asymmetry of the breath sounds confirms the diagnosis of tension pneumothorax and makes a disambiguation from pericardial tamponade possible. As has been indicated above, this distinction is critical because the treatment of the two life-threatening conditions is quite different.
Because these conditions are necessarily diagnosed by clinical, physical examination, there is a critical need for a manikin that allows the trainee to learn and practice the rapid physical diagnosis and the correct treatment of tension pneumothorax and cardiac tamponade and to reassess the simulated patient for the reversal of the abnormalities caused by these conditions immediately after treatment.
Since both conditions can cause rapid patient death, expertise in their differential diagnosis and treatment should be assured in practitioners certified in any form of advanced life support. Thus, it is desirable to integrate sensors into the manikin that provide objective data to permit assessment of trainee performance. Sensors that permit assessment of the timeliness and correctness of diagnosis and treatment would be particularly desirable.
Because of the above considerations, there is a critical need for improved systems for simulating the diagnostic features of tension pneumothorax and cardiac tamponade within medical training manikins.